Megasquirt users, how are you driving your OE Tacho

[Woznaldo]

As per the title I'm trying to work out how the MS users in the club are driving their tachos.

I'm running MS1 extra on a V2.2 board with EDIS4 ignition. I've got a post in the MS1 Extra support forums but as it depends on what tacho your are running, I thought the answer may be a little closer to home.

[SCHWARTZ]

Isn't there a driver you can buy for fourpots? Looks like 2 wires into 1 with a resistor in the middle or something. Then you can cut the blue (i think) wire off the back of the clocks like what you do with the b18ft loom.

[Woznaldo]

Yes there is but I'd like to drive it off the EDIS module if I can. I've got a reply from the MSExtra forum and been advised to try Pin 2 (EDIS) first and see what happens.

It all depends on what the OE tacho requires to drive it (voltage of the pulses).

[SCHWARTZ]

It will be good to see what you find out as I will be going megasquirt soon but will be using standard coil and tdc sensor etc...

[markey b]

2x diodes into 1, i'll get the info, i think i have some diodes spare, i had to do this on the KA when i put a zetec in so that the rev counter didn't read 'half'

[markey b]

http://www.fk-oc.com/e107_plugins/forum/forum_viewtopic.php?31527

[Scoff]

I tried driving a GTT tacho with EDIS4 once before, it didn't work so I had to connect it to the ECU instead.

[SCHWARTZ]

Yeah that's the kinda thing I'm on about mark.

[markey b]

Yeah that's the kinda thing I'm on about mark.

if u need any diodes lemme know i have squillions, i ended up buying about 20 in the end to make one as it was cheaper to buy bulk than just 2

[SCHWARTZ]

Cheers fella il bear that in mind;)

[Woznaldo]

http://www.fk-oc.com/e107_plugins/forum/forum_viewtopic.php?31527

Mark, I did read this for other cars on the MSExtra forum so sounds like it might be the way to go, especially if Scoff was having dramas too!

[Woznaldo]

I tried driving a GTT tacho with EDIS4 once before, it didn't work so I had to connect it to the ECU instead.

Did you try Pin 2? Just try to rule it out before I start.

[markey b]

Mark, I did read this for other cars on the MSExtra forum so sounds like it might be the way to go, especially if Scoff was having dramas too!

i wired it off the plug to the coil, the 2 outer pins just chipped into the wiring and ran to tacho

[Scoff]

i wired it off the plug to the coil, the 2 outer pins just chipped into the wiring and ran to tacho

On the ford coil you mean ? You will have had to couple to those via resistors, is that what you did ? Not just connect them together obviously :)

[markey b]

On the ford coil you mean ? You will have had to couple to those via resistors, is that what you did ? Not just connect them together obviously :)

yea ford coil, via two diodes so you get a 4cyl pulse without backfeeding the coil. i think megasquirt actually do a loom for it but its 20p in diodes to make your own

[SCHWARTZ]

Triggerwheels do one 2 wires into 1 with diodes in middle about 9odd quid.

[markey b]

Triggerwheels do one 2 wires into 1 with diodes in middle about 9odd quid.

thats the kiddy! 20p to make though

[Woznaldo]

I've just made one up after buying a pack of 50 diodes for about 4 quid. Yet to be tested but at least I'll have 48 spares. :)

[Woznaldo]

Ok, I've finally got around to trying the diode setup off the coil pack to drive the tacho and it's working! I also tried pin 2 and 11 (this is all using an EDIS4 setup) but, no luck.

I went with 2 x 1N4004 diodes and a 15-18v Zener diode and I've got a nice clean signal and the tacho is stable.

It took a while to actually get this far due to spark issues and an idle problem:

http://www.rtoc.org/boards/showthread.php?t=31041